The property of the alkaline earth metals that increases with their atomic number is

Which of the following elements does not exhibit variable valency?

Name an element from Group $2$ which forms an amphoteric oxide and a water soluble sulphate.

Identify the correct statements with respect to compounds of Beryllium:
$I$. Beryllium oxide is amphoteric in nature.
$II$. Beryllium hydride is formed by the reaction of beryllium with hydrogen.
$III$. Beryllium hydride is formed by the reaction of beryllium chloride with lithium aluminium hydride.
$IV$. Beryllium sulphate is the least soluble sulphate among the sulphates of alkaline earth metals.

An element of group $2$ forms a covalent oxide which is amphoteric in nature and dissolves in water to give an amphoteric hydroxide. Identify the element and write chemical reactions of the hydroxide of the element with an alkali and an acid.

Which of the following is dolomite?